The invention relates to an apparatus for recording and/or reproducing signals in a plurality of parallel longitudinal tracks on a magnetic tape. Such apparatus includes a head support which carries a magnetic head having a head face across which the magnetic tape is moved during operation and having air gaps, which terminate in a scanning portion of the head face, for scanning the respective tracks on the magnetic tape. The position of the magnetic head relative to the magnetic tape is adjustable by means of a positioning device which comprises first and second positioning systems which comprise piezo-electric elements, by which first positioning system the magnetic head is movable in a first direction relative to the magnetic tape and by which second positioning system the magnetic head is pivotable in a second direction relative to the magnetic tape by pivoting about a pivotal axis which extends substantially perpendicularly to a plane tangential to the scanning portion of the head face. The positioning systems are controlled by first and second control means respectively for generating and applying a control signal to the piezo-electric elements of the respective positioning systems, which control signal is representative of the difference between the instantaneous and the desired position of the magnetic head relative to the magnetic tape.
In order to increase the number of tracks and thus the useful effect of the signal storage on the magnetic tape, the track widths and the track spacings are continually being reduced. As an example, equipment has been developed with which the signal storage on the magnetic tape is effected in more than 100 tracks having a track width of approximately 40 micrometers, and a track spacing of approximately 10 micrometers. It is obvious that in this type of equipment slight displacements of the magnetic tape relative to the magnetic head in the width direction of the tape are sufficient to prevent the respective air-gaps of the magnetic head from following the associated tracks with the desired accuracy. Thus, the accuracy with which a magnetic head can be positioned is a factor which also determines the minimum attainable width of the track and the track-to-track spacing.
In such apparatus it is further essential for satisfactory reproduction that the respective air gaps of the magnetic head as they follow the tracks are continuously so positioned relative to the track that the time relationship between the respective tracks is maintained constant within narrow limits. This time relationship may then be disturbed by tilting of the magnetic tape relative to the magnetic head (so-called "skew").
In order to comply with the stringent position requirements, apparatus of this type are provided with positioning devices which control the position of the magnetic head relative to the magnetic tape. Such an apparatus is for example known from British Patent Specification No. 925,603. The positioning device of this known apparatus comprises two positioning systems, of which a first positioning system is adapted to correct an irregular speed of transport relative to the magnetic head (so-called "wow-and-flutter"). This correction is effected by pivoting the magnetic head around a pivotal axis which is directed perpendicularly to the longitudinal axis of the magnetic tape. In the way the first positioning system is not capable of correcting for displacements of the magnetic tape in the width direction of the tape. A second positioning system has been provided for maintaining an optimum time relationship between the respective tracks, which second positioning system comprises only one piezo-electric element, which extends parallel to a plane which is perpendicular to the direction of transport of the magnetic tape. Because of this arrangement of the piezo-electric element, this positioning system is sensitive to frictional forces as a result of the friction between the magnetic tape and the magnetic head. These frictional forces unfavorably load the positioning system, so that the desired accurate positioning in order to maintain the time relationship between the tracks cannot be attained under all circumstances. The method of arranging the magnetic head on the piezo-electric element of the second positioning system furthermore may permit to damage of the piezo-electric element as a result of, for example, an impact load which occurs in the case of irregular tape transport. Owing to these unsatisfactory positioning facilities the known apparatus is not suitable for following tracks with a small track spacing.